Balanced automatic volume control



Sep ,1 5- s. BALLANTINE BALANCED AUTOMATIC VOLUME CONTROL Filed Aug. 50,1932 .4 Sheets-Sheet 1 INVENTOR STUART A NTINE BY m ATTORNEY S.BALLANTINE BALANCED AUTOMATIC VOLUME CONTROL Filed Aii so, 1952,

4 Sheets-Sheet 2 QQ Q7 INVENTOR STUART BALLANTINE Sept. 1 7, v l 935.

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s. BALLANTINE 2,014,831 BALANCED AUTOMATIC VOLUME CONTROL Filed Aug. 30,1932. 4 Sheets-Sheet 4 fizzy 5 iNVENTOR STUART BA NTINE BY IHZM A'TTRNEYPatented Sept. 17, 1935 UNITED STATES PATENT OFFICE BALANCED AUTOMATICVOLUME CONTROL Stuart Ballantine, Mountain Lakes, N. J., assignor toRadio Corporation of America, a corporation of Delaware ApplicationAugust 30, 1932, Serial No. 631,000

11 Claims.

amplifiers especially adapted for use in radio re,-

ceivers.

One of the main objects of my present invention is to provide anautomatic volume control arrangement for use in a radio receiver whereinthe coupling between the source of signal energy and the radio frequencyamplifier of the receiver is controlled automatically by the amplifieroutput energy in such a manner that a substan-. tially constant carrierlevel is maintained at the amplifier output.

Another important object of my present invention is to provide incombination with a source of signal energy to be amplified and anamplifier for the energy, a control arrangement which is adapted tomaintain the transfer of energy between the source and the amplifiersubstantially constant, the said energy transfer being varied in aninverse mannerwith respect to the amplifier output.

Still another important object of the present invention is toprovide incombination with an automatic volume control circuit of the type whichautomatically controls the radio frequency input to a. radio frequencyamplifier, an automatic gain control circuit which is adapted to controlthe amplification of theaforementioned amplifier in order to provide abalanced automatic volume control arrangement.

Another object of the present invention is to provide a radio receiverwhich includes a source of signal energy and a radio frequencyamplifier, an automatic volume control arrangement comprising a normallyunbalanced bridge arrangement arranged between the signal energy sourceand the amplifier input, the bridge being electrically associated withthe amplifier output in such a manner that the amplifier output ismaintained substantially constant regardless of fluctuations of thesignal energy carrier, the receiver additionally including an automaticgain control arrangement connected between the amplifier input and itsoutput whereby the amplification of the amplifier is controlled in apredetermined manner as the energy transfer to the amplifier input iscontrolled.

Still another object of the present invention is to provide a bridgetype automatic volume control arrangement for a radio receiver whereinthe bridge includes an electron discharge tube as an arm thereof, andthe bridge is arranged between the antenna and radio frequency amplifierof a radio receiver, the amplifier output being utilized to provideenergy for controlling the conductivity of the bridge tube whereby thetransfer of energy from the antenna to the amplifier may be auto- 5matically controlled.

Still other objects of the present invention are to improve generallyautomatic volume control arrangements, and to particularly provideautomatic volume control circuits for radio receivers 10 which are notonly durable and reliable in operation, but economically manufacturedand assembled in radio receivers.

The novel features which I believe to be characteristic of my inventionare set forth in par- 15' ticularity in the appended claims, theinvention itself, however, as to both its organization and method ofoperation will best be understood by reference to the followingdescription taken in connection with the drawings in which I have 20indicated diagrammatically several circuit organizations whereby myinvention may be carried into effect.

In the drawings,

Fig. 1 shows in schematic fashion a radio re- 5 ceiver embodying oneembodiment of the invention,

Fig. 2 shows a modified form of the invention,

Fig. 3 shows a modification of the arrangement shown in Fig. 2,

Fig. 4 shows still another modified form of the invention shown in Fig.2, and

Fig. 5 shows a modification of a control portion of the arrangementshown in Fig. 2.

Referring now to Fig. 1 of the accompanying drawings, which showsschematically a portion of a conventional radio receiver embodying aform of the present invention, it is pointed out that the numeral Irepresents a conventional type of radio frequency amplifier whose outputis to be controlled so as to be of a substantially constant level inspite of the fluctuations of the carrier level in the input energysupplied to the said amplifier. The input circuit of the amplifier l isshown as of the tunable type, and comprises an inductance coil 2 shuntedby a variable tuning condenser 3, the inductance 2' being showninductively coupled to a pair of inductive arms 4, 5 of a Wheatstonebridge arrangement.

The antenna, or other signal energy collecting means A is connected toone point a of the bridge, while the diagonally opposite point b isgrounded. Point 0 of the bridge, the ungrounded terminal of inductivearm 4, is connected to point a through 55 a resistive arm 6 of thebridge, the resistor 6 being shunted by a condenser I.

The fourth arm of the bridge comprises the plate to cathode capacity 8(shown in dotted lines) of an electron discharge tube 2, the oathode oftube 2 being connected to the ungrounded end of inductive arm 5, and theplate of tube 2 being connected to the point a of the bridge. The plateof tube 2 is maintained at a positive potential through a path whichincludes the radio frequency choke coil L and source of potential I5.The high potential side of the output circuit of amplifier I isconnected, through a lead 9 and condenser I4, to the grid of an electrondischarge tube I, while the cathode of tube I is connected to the lowpotential side of the output of amplifier I. Tube I is biased for platerectification by means of battery I3 and resistor I2.

The anode of tube i is connected to its cathode through a path whichincludes a potential source I 0 in series with a resistor R1, thepositive terminal of source I B being connected to the anode of tube I.The cathode of the bridge tube 2 is connected to the cathode of tube I.The control electrode of tube 2 is connected, through a path whichincludes the resistor R, to the junction of resistor R1 and the negativeside of the potential source III. A condenser 01 is connected across thecontrol electrode and cathode of tube 2 and a condenser C2 is connectedacross the resistor R1. The grid of tube 2 is biased by means of batteryII which also overcomes the drop in R1 due to the steady current in tubeI.

The symbol 60 represents the signal input potential impressed across thebridge input circuit of amplifier I between antenna point a and groundpoint I). The symbol 6g represents the output energy potential deliveredto the input of the next stage succeeding the amplifier I. The nextstage may be a detector circuit, or an additional tuned radio frequencyamplifier circuit. The purpose of the arrangement shown in Fig. 1 is tomaintain e substantially constant in spite of fluctuations in the levelof 60.

This is accomplished by normally maintaining the antenna bridge circuit,which is coupled to the tunable input circuit of amplifier I,unbalanced. That 1s, the constants of the bridge are so chosen that apredetermined degree of unbalance is secured for a desired value of eg.Obviously, when the bridge is unbalanced the signal collecting means Awill be capable of delivering signal energy to the amplifier I. However,as soon as the carrier potential level increases above that value whichwill result in the desired value of eg, then the conductivity, orconductance g of tube 2 will be varied by the control tube I in such amanner that the bridge will approach balance and the input energydelivered to the amplifier I be decreased.

Conversely, if the carrier potential level falls below the desiredlevel, then the control tube I will function to vary the conductance oftube 2 in that direction which will still further unbalance the bridgeand increase the energy delivered to the input of amplifier I. In thisway it will be seen that the path between the output of amplifier I andthe input bridge, which includes tubes I and 2, functions toautomatically control the transfer of energy from the signal collectingmeans and the input of the amplifier I in such a manner that the value eis maintained substantially constant. The tube 2 functions as a variableradio frequency conductance which depends on the direct currentpotential applied to its grid. This, in turn, depends upon the rectifiedoutput of the control, or rectifier, tube I.

In Fig. 2 is shown a modified form of the invention wherein thebridge-type automatic volume control of Fig. 1 is combined with gridbias type automatic volume control. That is, the signal collecting meansA is again connected to the point a of the bridge, while the point I),at the junction of the inductive arms 4 and 5, is grounded. The tube 2comprises the fourth arm of the bridge, the cathode of tube 2 beingconnected to the ungrounded terminal of the inductive arm 5 in thiscase, while the grid of tube 2 is connected to a point on resistor R1through resistor R. The anode of tube 2 is maintained at a positivepotential through a path which includes the radio frequency choke coilL, by connecting it to the positive terminal of a source of anodepotential B, which source is not shown, direct current blockingcondensers being connected between point a and the antenna circuit A andbetween point a and the resistor 6.

The anode of rectifier tube I is connected by a lead II to the lowpotential side of coil 2, while the rotor of tuning condenser 3 isconnected to ground point b through a lead I2. The radio frequencyby-pass condenser I3 is connected between the lead I2 and the lowpotential side of inductance 2, and a condenser I4 is connected betweenthe grounded side of condenser 3 and the grid voltage lead to tube 2, acondenser I5 also being connected in shunt with the grid and cathode oftube 2.

A lead I6 connects the point of zero potential of resistor R1 to thecathode of the amplifier I through a bias potential source 20. The inputelectrodes of rectifier tube I are connected across the output circuitof amplifier I, the grid of tube I being connected through a condenserI6 to the 40 high potential side of amplifier I, while the oathode oftube I is connected through potential sources I! and I8 to the lowpotential side of amplifier I. A resistor R2 is connected from the gridof tube I to the negative side of potential source I'I, while a lead I9is connected between the low potential side of resistor R1 and the lowpotential side of amplifier I.

In considering the operation of the arrangement shown in Fig. 2 it willbe seen that the transfer of signal energy to the tunable input circuitof amplifier I is controlled by the state of balance of the Wheatstonebridge arrangement, and that the amplification, or gain, of theamplifier I is additionally controlled. In other words, the rectifiedoutput of rectifier tube I not only controls the conductance of bridgetube 2 so as to vary the state of balance of the antenna bridge, butalso controls automatically the bias of the grid of amplifier I.

Thus, when the ouput of amplifier I increases above the desired value ofeg, the potential drop across resistor R1 increases, with the resultthat the anode side of resistor R1 becomes more negative therebyincreasing the negative bias on the grid of amplifier I. This results ina decrease in the amplification of amplifier I. At the same time, theconductance of tube 2 is varied in a direction such that the antennabridge will approach a balance condition, thus reducing the transfer ofenergy to the amplifier I. Should the signal energy level 60 decreasebelow that value which is desired, then the reverse action occurs withthe result that the value of e is maintained substantially uniform.

While the operation of both types of automatic volume control have beenexplained as simultaneous, it is to be clearly understood that thecircuits may be arranged sothat the control action on the grid ofamplifier I does not commence until after the control action on tube Ihas progressed to a considerable extent, and from that point on thesetwo control actions may continue simultaneously. Again, it is quiteevident that the two control actions may be successive, one notbeginning until the other has ended.

In'any event, the essential feature of the present composite, orbalanced, automatic volume control system results in a type of automaticvolume control action wherein the antenna bridge may not, afterapproaching a. state of balance, be thrown into a state of unbalanceagain, by a continued increase of the value of e As shown at present thetwo control systems (bias control in amplifier and bridge balance) mayoperate simultaneously, or may be made to operate at different rates. Byproperly selecting anode and bias voltages, and setting the taps on R1the bridge may be made to approach bal- 4 ance slowly while theamplifier gain may change rapidly as the control bias increases, oragain the bridge may be made toapproach balance rapidly and remainapproximately balanced for increasing negative grid bias while theamplifier gain is reduced continually as the control bias increases. Thecontrol action is more or less overlapping of course.

In Fig. 3 is shown a modified form of composite automatic volume controlarrangement of the type shown in Fig. 2. The amplifier to be controlledcomprises a 224 screen grid tube having its control electrode connectedto the high potential side of the amplifier input circuit 2, 3 through acondenser 20 having a magnitude of the order of 100 micro micro-farads.The cathode of tube is connected to the low potential side of theresonant circuit through a bias resistor 2|. It should be noted that thelow potential side of the circuit 2, 3 is grounded, and connectedthrough a fixed condenser 22 to the point b at the junction'of theinductive bridge arms 4, 5. The point D of the bridge is shown arrangedfor connection to ground volts), or, if

desired, to a source of voltage 38. The antenna A is connected to pointa, while a variable condenser 23, resistor 36 and direct currentblocking condenser 31 comprise one arm of the bridge, coils 4 andcomprise the second and third inductive arms, the fourth arm of thebridge comprising the bridge tube 2, also designated in Fig.

3 by the letter X.

The anode of the balancing tube 2 has positive potential applied to itfrom a source B (not shown) through a path which includes a choke coil24, one end of the choke coil being connected to point it while theother end is grounded through a condenser 25. The plate to cathodecapacity of tube 2 is shown in dotted lines, and is designated by thenumeral 8. The grid of tube 2 is connected by a lead 26 to a movable arm21 arranged to contact either of the pair of terminals 28, 29.

The terminal 28 is connected through a lead 30 to the high potentialside of resistor 2|, the resistor 2| being shunted to ground by aby-pass condenser 3|. The terminal 29 is connected to lead 32 which isconnected between the normal automatic volume control tube (not shown)and the negative side of the automatic volume control biasing resistorR1. The lead 33 and resistor 34 provide the normal automatic volumecontrol bias path between the grid of amplifier tube and the negativeend of the bias resistor R1. The low potential side of the leak resistor34 is by-passed by an appropriate condenser 35. 5

The anode of amplifier tube I is adapted to be connected to the grid ofthe succeeding amplifier stage, and the normal automatic volume controltube not shown in Fig. 3 is to be understood as comprising, if desired,the rectifier tube shown in Fig. 2. The rectifier tube i may employ forits input the output of amplifier tube I, or the output of a succeedingamplifier stage, or even the output of the receiver detector stage, inwhich case the automatic volume control tube functions as a directcurrent amplifier.

The operation of the arrangement shown in Fig. 3 corresponds to thatexplained in connection with Fig. 2. When the arm 21 is connected toterminal 29 then the output of the normal automatic volume control tubecontrols the direct current potential of the grid of the bridge tube X,and also the grid potential of the amplifier tube However, when the arm21 is connected to terminal 28, then the balancing bridge tube X has itsgrid potential derived from the positive side of the resistor 2| in thecircuit of amplifier I.

In this case the grid potential applied to the balancing tube X may beoperated at a positive voltage even though a relatively high current(compared to the current through R1) flows in the grid circuit of tubeX. In this case tube I' may be said to operate as a direct currentamplifier between the voltage source R1 and tube X, While it is alsooperating as the normal signal amplifier.

The reason for obtaining bias for tube 2 from resistance 2| rather thanfrom R1 when the grid bias of tube 2 is positive is that appreciablegrid 40 current fiows in tube 2 and this current is small compared tocurrent in 2 i, but large compared to current in R1. It would beimpractical to operate tube 2 directly from R1 when the grid bias oftube 2 is positive. ered as a direct current amplifier in that thedirect current voltage across the relatively high resistance R1 isconverted by tube to a direct current voltage across the relatively lowresistance 2| while at the same time tube is also being used as a radiofrequency amplifier.

Another modified form of composite automatic volume control arrangementis shown in Fig. 4; there is utilized in place of a Wheatstone bridgearrangement between the signal energy source and the controlledamplifier, an arrangement as shown in Fig. 4. In this figure thereceiver is shown as comprising the usual grounded antenna circuit Awhich is inductively coupled, as at M1,

to the tunable input circuit of amplifier tube M) which is of the screengrid type. The plate of tube at is arranged for inductive coupling tothe tunable input circuit of the succeeding screen grid amplifier 4|through a coil 42. One end of the coil 42 is connected to the positiveterminal oi the anode potential source B1, it being noted that thenegative terminal of this source is connected to the grounded cathodelead of tube 40. The grid circuit of tube 4|) includes a negativebiasing potential source C1, and the variable tuning condensers 43 and44 arranged respectively in the input circuits of tubes 49 and 4| aredisposed for mechanical uni-control as shown by the dotted lines 45. Thecoil 42 is coupled to the coil 42' of the tunable input circuit of thetube 4| The tube I may be consid- 45' A third inductance coil 45connected at one terminal thereof to the positive side of source B1, andits other terminal by means of a lead 46 to the plate of a screen gridbalancing tube 40, is also coupled to coil 42', but in a reverseddirection.

It will, therefore, be seen that the anode circuits of tubes 48 and 40'are inductively coupled to the tunable input circuit of tube 4|, andthat the control grid of tube 48' is connected to the grid circuit oftube 48, and to the high potential side of tuning condenser 43, througha path which includes the condenser 47. The cathode of tube 40 isconnected to the ground point of the cathode of tube 40.

It will now be seen that signal energy applied to the tunable inputcircuit of tube 40 is similarly applied through the radio frequencycondenser 41 to the control grid of balancing amplifier tube 40'. Theoutputs of tubes 49 and 49 are simultaneously impressed in oppositedirections, across the tunable input circuit of amplifier tube 4| sothat when the amplification of tubes 4D and 40 are equal, signalvoltages of equal amplitude, but opposite phase, are set up in coil 42and the combined signal output from the tubes 40 and 4!! in the circuit42, 44 is zero.

The application of output energy from amplifier tube 40 upon the tunableinput circuit of tube 4| may be controlled by means of a rectifier tube48 which has its control grid connected to the anode circuit of tube 41,or to the output of succeeding amplifier stages, through a radiofrequency condenser 49, the cathode of tube 48 being :cOnnected to thelow potential side of tube 4| through a path which includes the sourceB2, the resistor 59, and the lead A resistor 52 is connected between theanode of tube 48 and the resistor 59, and the positive terminal ofsource B2 is connected to one side of resistor 50, while the negativeterminal of source B2 is connected to the cathode of tube 48.

The cathode of tube 48 is connected to the control grid of tube 48through a path which includes biasing potential source C2 and a resistor53 connected in series between the said control grid and the negativeterminal of the source C2. The anode of tube 48 is connected to thecontrol electrode of the amplifier tube 4| through the leak resistor 55,while the control grid of balancing tube 4|) is connected to a point Ecoof the source B2 through the resistor 55.

The operation of the arrangement shown in Fig. 4 may be explained in thefollowing manner: When the signal energy level in the output of tube 4|increases above the desired level, the output of rectifier tube 48increases with the result that the negative potential applied throughlead 54 to the grid of tube 4| increases, while the positive controlpotential applied to the grid of balancing tube 40 through resistor 55increases. This results in a greater fiow of current through the coil45, and consequently results in a decrease in energy transfer from theoutput circuit of amplifier 40 to the input circuit of controlledamplifier 4|. Simultaneously, of course, the amplification of tube 4|has decreased and as explained heretofore, the two control actions maybe successive, or overlapping, in relationship. Should the energy outputof tube 4| decrease below the desired level, then the reverse actionwould take place, and the energy delivered to the tunable input circuitof tube 4| would be increased, while the amplification of tube 4| isincreased.

The outputs of tubes 40 and 40 are coupled to the input circuit of tube4| in reversed directions so when the outputs from 40 and 40' are equalthey balance, and no input signal is transferred to tube 4|. or 40' ischanged the outputs no longer balance and a signal is passed on to tube4|, the magnitude of which depends on the degree of unbalance. Normally,(as shown in Fig. 4) with no input signal in A, tube 40 is biased for ahigh amplification (lowbias), and tube 40 is biased for lowamplification (high bias). When signal at A increases to such a valuethat the output from 4| (or succeeding stages) operates automatic volumecontrol tube 48, the bias of tube 40 is made lower (more positive) bythe voltage across 50, and the output signal from 4|! increases inopposition to the output from 40, thereby lowering the combined outputfrom 40 and 40.

This continues with increasing input at A until the amplification of 48'equals that of 40, when the outputs balance out, and the combined outputis zero. This operation may be reversed by biasing tube 40 for lowamplification (high bias) and tube 40 for high amplification (low bias).Then, to approach balance in the combined outputs of and 40, as thesignal input at A increases, the bias of 40' would be increased(negatively) which both lowers the amplification of 40' and approaches abalance in the combined outputs. 30.

Normal amplification reduction in amplifier 4| occurs at the same time,of course, by the increasing negative bias supplied by 52. The balancingsystem will operate, then, when the amplification of either of the pairof tubes 40 and 40' change 36 relatively, which may be accomplishedby 1) maintaining one constant and changing the other, (2) changing bothin opposite directions, and (3) changing both in the same directions,but at different rates.

If desired, instead of controlling the lower tube 40, the upper tube 40may be controlled, and both tubes 40 and 40 may even be controlled bythe rectified output of tube 48. If the upper tube 40 is controlled bythe rectified output of tube 48, then all biases can move negatively together; that is to say, the bias applied to the control grid of tube 40and then applied to the control grid of tube 4| could both be in anegative direction, instead of being positive and negative respectivelyas shown in Fig. 4. Again, and as pointed out heretofore, the controlvoltage may be derived from the detector of the receiver, and the tube48 may then function as a direct current amplifier, the direct currentoutput in that case functioning as shown in Fig. 4 to control the biasesof tubes 40 and tube 4|.

In each of Figs. 1 to 4 inclusive there is shown various means forobtaining the control bias voltage, and it is to be noted that in eachof Figs. 1, 2 and 4 the bias is derived from a special rectifier tube.It has already been explained that instead of a rectifier tube, a directcurrent amplifier working out of the receiver detector may be employedfor supplying the control bias voltages. Obviously, there are othermethods of obtaining the control bias voltages. For example, a directcurrent amplifier may be employed in connection with the rectifier tube48 of Fig. 4, and the direct current amplifier output used to providethe control biases. Additionally, instead of employing an auxiliarydirect current amplifier tube, one of the radio frequency amplifiertubes of the receiver may be utilized to simultaneously function as thedirect current amplifier tube following the auto- When the amplificationof either 40 5 matic volume control rectifier. Again, and as shown inconnection with amplifier I in Fig. 3, the control biases may be derivedfrom a resistor arranged in the cathode lead of the detector.

In Fig. 5 there is illustrated an arrangement whereby the control biasfor the balancing tube 2 of Fig. 3, for example, may be derived from aresistor 60 arranged in the negative leg of the cathode of the detector,while the negative control bias for the controlled radio frequencyamplifier is derived from the potential drop across the resistor 6!arranged in the anode circuit of the usual automatic volume controlrectifier 62. The voltage supply of cathode, control grid and anode ofrectifier tube 62 is derived from across the B supply potentiometer 63,and the input energy for the rectifier 62 is derived from the source ofenergy connected to the input electrodes of the detector tube. Thenegative control bias derived from the drop across resistor 6| isutilized, as pointed out heretofore, for controlling the bias of theradio frequency amplifier.

Instead of using a triode as a control rectifier, it is also possible touse a tetrode, in which case the control grid of the balancing tube 2would be connected to the control grid of the tetrode, and the potentialdrop across the biasing resistor in the tetrode anode circuit wouldsupply the negative control bias for the amplifier grid, the auxiliarygrid adjacent the anode being utilized in this case to have signalenergy impressed thereon from the controlled amplifier output circuit.

While I have indicated and described several systems for carrying myinvention into effect, it will be apparent to one skilled in the artthat my invention is by no means limited to the particular organizationsshown and described, but that many modifications may be made withoutdeparting from the scope of my invention as set forth in the appendedclaims.

What I claim is:

1. In combination with an amplifier, and a source of signal energy, anormally unbalanced bridge circuit arrangement arranged between thesource and the amplifier input, and means including a signal rectifierconnected between an arm of said bridge and the output of the amplifierfor controlling the bridge balance thereby to automatically adjusttransfer of energy from said source to said amplifier.

2. In combination with an amplifier, and a source of signal energy, anormally unbalanced bridge circuit arrangement arranged between thesource and the amplifier input, and means including a signalrectifierconnected between an arm of said bridge and the output of the amplifierfor controlling the bridge balance thereby to automatically adjusttransfer of energy from said source to said amplifier, said bridge armcomprising an electron discharge tube.

3. In combinationwith an amplifier, and a source of signal energy, anormally unbalanced bridge circuit arrangement arranged between thesource and the amplifier input, and means connected between an arm ofsaid bridge and the output of the amplifier for controlling the bridgebalance thereby to automatically adjust transfer of energy from saidsource to said amplifier said bridge arm comprising a variable radiofrequency conductance, and said means comprising a rectifier tubeconnected between said conductance and the output circuit of theamplifier.

4. In combination with an amplifier, and a source of signal energy, anormally unbalanced bridge circuit arrangement arranged between thesource and the amplifier input, and means connected between an arm ofsaid bridge and the output of the amplifier for controlling the bridgebalance thereby to automatically adjust transfer of energy from saidsource to said amplifier, and additional means connected between saidcontrol means and amplifier input circuit for controlling theamplification of the amplifier.

5. In combination, in a radio receiver, a source of signal energy, anamplifier, a normally unbalanced bridge connected between the antennaand the amplifier input circuit, said bridge including an electrondischarge tube as an arm thereof, a rectifier connected to the outputcircuit of said amplifier, and means for connecting the output circuitof the rectifier to the bridge tube and the amplifier in such a mannerthat the transfer of signal energy to the amplifier, and theamplification thereof, are controlled in accordance with variations inthe amplifier output circuit.

6. In combination, in a balanced automatic volume control arrangementfor a radio frequency amplifier, a source of signal energy, a bridgeincluding an electron discharge tube as an arm thereof arranged betweensaid source and said amplifier, means for controlling the bias of theamplifier grid, and an automatic volume control tube connected betweensaid, bridge tube, biasing control means, and the amplifier outputcircuit.

7. In combination, in a radio receiver, a radio frequency amplifier, apreceding radio frequency amplifier coupled to said first amplifier, acontrol tube having its input circuit connected to the input circuit ofsaid preceding amplifier, and its output circuit coupled to saidpreceding amplifier output circuit and first mentioned amplifier inputcircuit, and a control rectifier connected between the first mentionedamplifier output circuit, the grid of said control tube, and grid ofsaid first mentioned amplifier.

8. In combination with a radio frequency signal amplifier, a controltube arranged to regulate the transfer of signal energy to the inputcircuit of the amplifier, a detector tube having its input circuitcoupled to the amplifier, an impedance in the detector space currentpath for developing a direct current voltage whose magnitude depends onthe received signal amplitude, means for varying the gain of saidcontrol tube with said voltage thereby to relate said transferregulation to said signal amplitude, a signal rectifier arranged toproduce a uni-directional voltage from received signals, said lastvoltage varying in magnitude with changes in signal amplitude, and meansfor applying said last voltage to a gain control electrode of saidsignal amplifier for varying the gain thereof.

9. In combination with source of signal modulated carrier energy and afollowing amplifier of said energy, said amplifier being provided withan input circuit resonant to the frequency of said carrier, atransmission network coupled between said source and resonant inputcircuit, said network including at least one space discharge device, arectifier network connected to the output circuit of said amplifier, acontrol connection between the rectifier network and a gain controlelectrode of the said amplifier for varying the amplifier gain inresponse to the rectified current variations, and a control connectionbetween the rectifier network and said device for varying theconductivity of said device in response to fluctuations in the intensitylevel of said carrier energy, said transmission network includingadditional elements so related to said device that the carrier energytransmission therethrough decreases when the conductivity of said deviceincreases.

10. The method of controlling the output energy of a vacuum tubeamplifier which comprises simultaneously varying the bias potentialapplied to the input circuit of the tube and the amount of input signalsupplied thereto in response to variations in the amplitude of saidinput signal.

11. The method of controlling the output energy of a vacuum tubeamplifier which comprises controlling the gain of the tube and theamount of input signal supplied thereto in response to variations in theamplitude of said input signal.

STUART BALLANTINE.

